One easy and frugal way to get lots of pots for seed starting is to make them from things you may find around your house. Making seed starting pots from newspaper is not only very cheap but you're keeping trash out of landfills. To make your own seed starting pot is very simple. First, take a sheet of newspaper and fold it in half so that it is about the length of a can of soda (or "pop" as we say in Chicago) and then just roll the soda can until it wraps around the can. After that just fold in one end of the newspaper to make the bottom and you have a quick and cheap pot for starting seeds that you made from newspapers that you were just going to throw away.
In the photo below I used this technique to start some Amaryllis seeds, but you can do just about any seeds you want. When the seedlings have sprouted you can plant the whole thing in the ground where the newspaper will eventually decompose.
You can also create your own seed pots from toilette paper rolls. One good alternative I like when I only have a few seeds to work with is to make them from the tubes of gift wrapping paper. They're usually much sturdier than the tubes for paper towels or toilette paper. These seed pots can also be completely planted in the ground or into your container gardens.
Tip: set all of your homemade pots inside a take out container, if you don't have seed starting trays, so that they're touching. When you water fill the container with water and allow the water to be absorbed by the paper pots. If you're very eco-friendly make sure the newspaper you use prints with soy based ink.
Other things around your house you can use are yogurt cups, cut a water bottle in half and poke holes in th bottom for drainage, plastic containers from restaurants, Styrofoam cups from fast food restaurants or instant soup.
If you're feeling extra crafty you can also fold more complex seed starting pots by searching the internet. If you have more space and want a use for empty soda bottles make your own mini- ghetto greenhouse to start all of your seeds.
Square Newspaper Seed Starting Pots.
Homemade seed pots.
Starting seeds in soda bottles.
Paper tube seed pot holder.